Surface topography detection based on an optical differential metasurface

Dielectric Metasurfaces for Broadband Phase-Contrast Relief-Like Imaging

The visualization of transparent specimens in traditional light microscopy is impeded by insufficient intrinsic contrast, prompting the development of advanced contrast-enhancement methodologies to transmute minute phase discrepancies into detectable amplitude alterations. While existing methods excel in either phase-contrast imaging (contrast-enhanced image of whole objects) or relief-like imaging (deceptive three-dimensional images), it would be of great significance to seamlessly integrate both capabilities in the same device. Here, we propose a novel metasurface-assisted half-side phase-contrast technique capable of simultaneous phase-contrast and relief-like imaging across the visible spectrum, which is realized by introducing a ±π/2 phase shift to a half-side diffracted wave emitted by the objects. Our method showcases successful application to diverse specimens, including a transparent silica disk and a frog egg cell. Our work substantiates high-quality microscopic imaging of various transparent specimens, which has profound implications in cellular biology, materials science, and medical diagnostics.

Ultra-high order mode-assisted optical differentiator for edge detection with high tunability

An optical spatial differentiator based on the photonic spin Hall effect (PSHE) with high tunability is presented. By utilizing the characteristics of ultra-high order modes in the symmetrical metal cladding waveguide, the Fresnel reflection coefficient spectrum exhibits a narrow peak width and low trough at the resonant incident angles, resulting in high sensitivity to changes in the incident angle-induced spatial shift caused by the PSHE (the highest ∂(|r s/r p|)/∂ θ value can reach 107). After polarization transformation and extinction, the output field demonstrates differential operation with respect to the input field. When applied to edge detection, our differentiator can achieve tunable resolution edge images by adjusting the incident angle. Our proposed edge detection scheme has potential applications for cellular and molecular imaging through two-dimensional extension via the target rotation.

Metalens for Accelerated Optoelectronic Edge Detection under Ambient Illumination

Analog systems may allow image processing, such as edge detection, with low computational power. However, most demonstrated analog systems, based on either conventional 4-f imaging systems or nanophotonic structures, rely on coherent laser sources for illumination, which significantly restricts their use in routine imaging tasks with ambient, incoherent illumination. Here, we demonstrated a metalens-assisted imaging system that can allow optoelectronic edge detection under ambient illumination conditions. The metalens was designed to generate polarization-dependent optical transfer functions (OTFs), resulting in a synthetic OTF with an isotropic high-pass frequency response after digital subtraction. We integrated the polarization-multiplexed metalens with a polarization camera and experimentally demonstrated single-shot edge detection of indoor and outdoor scenes, including a flying airplane, under ambient sunlight illumination. The proposed system showcased the potential of using polarization multiplexing for the construction of complex optical convolution kernels toward accelerated machine vision tasks such as object detection and classification under ambient illumination.